This checklist is for people like me—the ones who sign the PO and then have to explain the final number to finance. If you're pricing a Perkins generator (40kW, 350kW, anything in between), you already know the base price isn't the total. The question is: how far apart are they?
I've been tracking generator purchases for our facility for about 6 years now—somewhere around $180,000 in cumulative spending. Here's the checklist I use to keep surprises off my desk. Three steps. Apply in order.
Step 1: Baseline the "Installed" Price, Not the Generator Price
The first quote you get is almost always the generator alone. Maybe with a basic controller. That's not what you'll pay.
What to check:
- Delivery and rigging: Is the quote FOB origin or delivered to your site? We've paid $800 to move a 350kW unit from a truck to the pad. Not extreme, but it wasn't in the quote.
- Fuel tank: Sub-base tanks are standard for larger units, but double-check. A 40kW unit might need a separate day tank.
- Transfer switch (ATS): This is the big one. An automatic transfer switch can add $1,500–$5,000 depending on amperage and brand. If your quote doesn't list it, ask.
- Permits and inspections: Local codes vary wildly. I don't have a national average, but in my experience, permit fees for a 350kW install in a commercial building run $500–$1,200. Get your contractor's estimate.
I wish I had tracked permit costs more carefully across our projects. What I can say anecdotally is that they've been the item most often missing from initial quotes. That's an easy way to blow your budget by 5% before you even start.
Step 2: Calculate the 5-Year Maintenance Trajectory
This is where the cost conversation gets interesting—and where most buyers I've talked to neglect the math. A Perkins diesel generator is a long-term asset. Maintenance is predictable, but it's not free.
Break it down by component:
- Oil and filters: A 40kW unit takes roughly 10–15 quarts of oil. A 350kW unit takes 30–40 quarts. Factor in two oil changes per year with standard use (plus the filter—if you've ever wondered how to take off an oil filter, the answer is usually a filter wrench and patience, but the cost is about $15–30 each).
- Fuel and water separators: Replace annually. Not expensive, but if you don't, injector issues show up fast. That's a much bigger bill.
- Battery replacement: Every 3–5 years. Two batteries for most standby units. A pair costs $200–400.
- Coolant system: Antifreeze changes every 2–3 years. Also inexpensive, but often forgotten.
- Load bank testing: This is the one nobody budgets for. Running a generator under load is the only way to know it actually works. For a 350kW unit, a rented load bank and a technician for a day is $1,000–$2,000. If you need to do this annually, build it into your budget.
What's the total? Roughly, a 40kW Perkins diesel generator will cost you $1,500–$2,500 a year in scheduled maintenance. A 350kW unit: $3,000–$5,000. These are my estimates based on our invoices. Your mileage will vary with load, runtime, and how hard you run it.
Honestly, I'm not sure why some vendors quote maintenance plans so differently. My best guess is they inflate the frequency to justify premium pricing. The manufacturer's schedule is your best baseline.
Step 3: Account for Downtime and the Cost of Not Having Power
This is the hardest number to pin down, and it's the one that justifies spending more upfront. If you're buying a 350kW Perkins diesel generator for emergency backup, what's the cost of a 4-hour outage?
Calculating it:
- Lost revenue per hour: If you're a manufacturing facility running 24/7, that might be $10,000–$50,000 per hour. If you're a commercial office with some sensitive servers, maybe $2,000–$5,000.
- Reputation damage: Hard to quantify, but a single multi-hour outage can lose a client. I've seen it happen.
- Spoilage: Cold storage? Freezers? Product loss adds up fast.
The upside of a Perkins generator is reliability. The risk is still real—any mechanical system can fail. I kept asking myself: is spending an extra $3,000 on a premium controller worth potentially saving two days of lost production? The answer was always yes after I ran the numbers.
Notes and Common Mistakes
Don't compare base prices without a scope of supply. Vendor A quotes $18,000 for a 40kW Perkins diesel generator. Vendor B quotes $22,000. Vendor B includes a 200-amp ATS, a 24-hour fuel tank, and delivery. Vendor A doesn't. That "cheaper" option just cost you more.
The vendor who lists all fees upfront—even if the total looks higher—usually costs less in the end. I've learned to ask "what's NOT included" before "what's the price."
Tax incentives and grants sometimes apply to standby generators. Not common, but check your local economic development office or utility company.
If you're looking at a kohler fuel pump rebuild kit or a generac portable generator from a local dealer, understand that the approach is different. For a Perkins generator, the supply chain for parts is well-established. For smaller portable units, availability can be more variable. I can't speak to every instance (I don't have hard data on generac portable generator dealers near me), but I've noticed it takes me more effort to source parts for non-industrial-grade equipment. Something to consider if your goal is long-term ownership.
This checklist won't make you a generator expert. But it'll help you ask the right questions before you sign. That's usually enough.
